1. Field of the Invention
The present invention generally relates to systems for manufacturing semiconductor integrated circuits and, more particularly, to pumping systems for evacuating reactor chambers that are used in the manufacture of semiconductor integrated circuits.
2. State of the Art
In the manufacture of semiconductor integrated circuits, it is typical to employ chambers from which air has been evacuated. During the evacuation of such reactor chambers, significant turbulent effects can be caused. When the reactor chamber is used in the manufacture of semiconductor integrated circuits, turbulence is highly undesirable. Specifically, during the manufacture of semiconductor integrated circuits, silicon wafers are generally introduced into a reactor chamber at atmospheric pressure and the reactor chamber is then degassed and the wafers are then treated with one or more reagents introduced into the reactor chamber which are used to modify the wafer.
In practice, turbulence can result in defects in the semiconductor integrated circuits. Specifically, particulate matter may collect within a reactor chamber by, for example, adhering to the walls of the reactor. Then, when turbulence is created within the reactor chamber, usually at the entrance to the evacuation line, particulate matter is caused to dislodge from the walls and can contaminate the wafers that are being processed. The wafer contamination can cause the semiconductor integrated circuits to be defective.
Workers in the art of fabricating semiconductor integrated circuits have attempted to control the turbulence that occurs in the reactor chamber as large volumes of fluid (e.g., air) in the reactor chamber are suddenly removed through the evacuation line. For instance, turbulence in evacuation chambers has been reduced by placing a valve in the evacuation line between the reactor chamber and a means for creating a partial vacuum includes a pump and a blower. The opening of the valve, shown in FIG. 1, is regulated such that, as evacuation begins, the valve is only slightly opened and flow is minimal. As the pressure drop across the valve decreases, the valve is slowly opened further, thus preventing large, turbulence-inducing flow rates. Also, a series of valves can be mounted in the evacuation line such that each set of two valves provides, in effect, a separate chamber. When it is desired to evacuate a reactor chamber, the opening of each valve can be set to produce a series of gradual pressure drops. However, in the case of the reactor chamber for semiconductor integrated circuits, the reactor chamber is typically at atmospheric pressure and a pump and blower causes a pressure drop to approximately 10 millitorrs. It has proven to be very difficult to control fluid flow in relatively large diameter evacuation lines, and these techniques for reducing turbulence during evacuation have produced largely unsatisfactory results. Turbulent effects have proven to be particularly in evidence when flow from the reactor chamber to the evacuation line is first being established.
In view of the shortcomings in prior art systems for controlling fluid flow in large diameter evacuation lines, workers in the art have attempted to reduce turbulence during evacuation of reactor chambers by connecting a second, smaller diameter line with a controllable valve between the reactor chamber and the portion of the main evacuation line near the means for creating a partial vacuum. Such solutions have, however, been found to be wanting in precision. Again, the large pressure drop that must occur between the opening to the slow pump line in the reactor chamber and the end of the slow pump line has been found to almost inevitably cause some turbulent effects in the reactor chamber. Further, it has been found that contaminants collect in the slow pump line itself and add to the contamination of the reactor chamber.